By many measurable parameters, transformed cells (TC) differ from primary cells in culture. Because of their ease of culturing, TC have been used extensively in experimental settings, notably, in vitro screening of new dental and medical materials for cytotoxicity and mutagenicity. However, advances in cell culture techniques have made possible routine growth and utilization of human primary cells (PC) for experimentation. These PC are more closely related to cells in the body than are TC. Therefore, human PC in culture are conceptually a more appropriate model for in vitro screening of new materials. This new direction comprises the central thrust of this application. The specific aims of this study are: (1) to grow human pulp fibroblasts, human skin fibroblasts, and transformed cells in culture under the same conditions; (2) to assess and compare growth characteristics of these cell types; (3) to assess and compare the baseline chromosome alterations of the cell types; (4) to measure the response of the cells to mutagenic stress; and (5) to measure the response of the cells to cytotoxic stress. Routine cell culture procedures will be used. This laboratory has long experience with primary cell cultures. TC lines previously used in materials testing will be evaluated and compared with PC response using cell culture growth parameters, three standard tests for cytotoxicity (agar overlay, succinate dehydrogenase histochemistry, and cloning efficiency), and two measures of chromosome integrity (chromosome breakage and sister chromatid exchange). Previously tested dental materials of known cytotoxicity will be used to offer the cytotoxic stress. This methodology should lead to improved testing of a wide variety of materials (implants, restorative, and prosthetic, for example) at minimum cost with optimal potential for correlation with in vivo tests. Decreasing the need for costly in vivo testing by accurate in vitro screening is an attractive goal. Indirectly, data obtained will be of benefit in the general area of pulp biology and the area of primary cell biology.